Total joint (knee, hip, and ankle) replacement prostheses are known in the art. In many instances, a specially designed jig or fixture enables the surgeon to make accurate and precise bone resections of the femoral surface, the tibial surface, or both in order to accept such prostheses. The ultimate goal with any total joint prosthesis is to approximate the function of the natural, healthy structures that the prosthesis is replacing. Should the prosthesis not be properly attached to the femur, tibia, ankle or foot, any misalignment could result in discomfort to the patient, gate problems, or degradation of the prosthesis.
For example, when attaching a knee prosthesis it is desirable to orient the prosthesis such that the pivot axis of the knee joint lies within a transverse plane that is generally oriented perpendicular to the mechanical axis of the femur. The mechanical axis lies along a line which intersects the femoral head and the center of the ankle. In the prior art, the mechanical axis had been determined from an inspection of a radiograph of the femur to be resected prior to, or even during the surgery. During the actual operation, the mechanical axis was determined by computing its valgus angle from the femoral shaft axis. It was then necessary to manually align any cutting guide and its fixtures with respect to the femoral shaft axis in order to achieve an optimum cut.
Often such cutting guides included a femoral intramedullary stem which was inserted through a pre-drilled passage way formed in the intercondylar notch and upwardly through the femur along the femoral shaft axis. The stem often included a bracket which supports a distal femur cutting guide. The bracket included a first pin which extended through the cutting guide to act as a pivot axis. A second pin was attached to the bracket so as to extend through an arcuate slot in the cutting guide. The cutting guide included pairs of opposing slots formed along its sides which were oriented to be perpendicular to a central axis of symmetry of the cutting guide. When the cutting guide was pivoted, such that the central axis of symmetry lay along the mechanical axis, so as to form the appropriate angle with the femoral shaft axis, the cutting guide slots were positioned to be perpendicular to the mechanical axis. The cutting guide was then locked into the predetermined angle with the femoral shaft axis.
In more recent times, computer-aided design techniques have been coupled with advances in imaging technology to improve joint replacement prostheses and methods. For example, in U.S. Pat. No. 5,735,277, a process of producing an endoprosthesis for use in joint replacement is disclosed in which a reference image for determining contour differences on a femur and a tibia, are obtained by comparing a corrected preoperative image of a damaged knee joint with a postoperative image. This technique is then used as the basis for preparing corresponding femoral and tibial components of an endoprosthesis.
In U.S. Pat. No. 6,944,518, a method for making a joint prosthesis is provided in which computed tomography, commonly known as a CAT scan (CT) data from a patient's joint is used to design a prosthesis. The CT data is downloaded into a computer aided design software in order to design at least an attachment part, and possibly a functional part, of the prosthesis. The attachment part can be used to attach or otherwise associate the functional part to the patient's bone.
In U.S. Pat. No. 5,370,692, a method for producing prosthetic bone implants in which imaging technology is used to define hard tissue characteristics (size, shape, porosity, etc.) before a trauma occurs (“pre-trauma” file) by archival use of available imaging techniques (computed tomography, magnetic resonance imaging, or the like). Loss of hard tissue is determined by imaging in the locale of the affected tissue after the injury (“post-trauma” file). The physical properties of the customized prosthetic device are specified by comparison of the pre-trauma and post-trauma files to produce a solid model “design” file. This specification may also involve secondary manipulation of the files to assist in surgical implantation and to compensate for anticipated healing process. The design file is mathematically processed to produce a “sliced file” that is then used to direct a manufacturing system to construct a precise replica of the design file in a biocompatible material to produce the implant.
In U.S. Pat. No. 5,798,924, a method for producing endoprosthesis where a data block of a three-dimensional actual model of existing bone structure of a patient is acquired using CT scanning. In a computer, the actual model is subtracted from the data block of an existing or CT scan-generated three-dimensional reference model. Then from the difference, a computer-internal model for the endoprosthesis is formed. The data blocks of the actual model and reference model are converted into the data of a CAD free-form surface geometry.
None of the forgoing methods or devices have adequately provided surgeons with a way to generate patient specific prostheses, surgical instruments, guides, and fixtures, nor have they aided in reducing the number or complexity of the fixtures used to locate resection guides in relation to the patient's body during orthopedic procedures, such as, total knee, hip, or ankle replacement surgery.